Since liquid crystal displays are thin and light, consume relatively little electrical power, and do not cause flickering like in cathode ray tube (CRT) displays, they have helped spawn product markets such as laptop personal computers. In recent years, there has also been great demand for liquid crystal displays to be used as computer monitors and even televisions, both of which are larger than the liquid crystal displays of laptop personal computers. Such large-sized liquid crystal displays in particular require that an even brightness and contrast ratio prevail over the entire display surface, regardless of observation angle.
Because the conventional twisted nematic (TN) mode liquid crystal display cannot easily satisfy these demands, a variety of improved liquid crystal displays have recently been developed. They include in-plane switching (IPS) mode liquid crystal displays, optical compensation TN mode liquid crystal displays, and multi-domain vertical alignment (MVA) mode liquid crystal displays. In multi-domain vertical alignment mode liquid crystal displays, each pixel is divided into multiple regions. Liquid crystal molecules of the pixel are vertically aligned when no voltage is applied, and are inclined in different directions when a voltage is applied.
Referring to FIG. 4, a typical multi-domain vertical alignment liquid crystal display (LCD) 100 includes a first substrate 110, a second substrate 120 parallel to the first substrate 110, and a liquid crystal layer 130 sandwiched therebetween. The liquid crystal layer 130 includes a number of liquid crystal molecules 130 having negative dielectric anisotropy.
The first substrate 110 assembly includes an upper polarizer 112, a first transparent substrate 111, a color filter 113, a common electrode 115, and a first alignment film 114 arranged in that order from top to bottom. The first substrate 110 further includes a number of first protrusions 141. Referring also to FIG. 5, the first protrusions 141 are arranged at an inner surface of the first alignment film 114 along generally V-shaped paths. The color filter 113 includes a number a red filters (not shown), a number of blue filters (not shown), and a number of green filters (not shown) sequentially arranged in that order.
The second substrate 120 assembly includes a lower polarizer 122, a second transparent substrate 121, a number of pixel electrodes 127, and a second alignment film 124 arranged in that order from bottom to top. The second substrate 120 further includes a number of second protrusions 142. The second protrusions 142 are arranged at an inner surface of the second alignment film 124 along generally V-shaped paths. The first protrusions 141 and the second protrusions 142 are arranged alternately.
Referring to FIG. 5, when the LCD 6 is in an off state, the liquid crystal molecules 131 are oriented perpendicular to the first substrate 110. In operation during the off state, incident light beams become linearly-polarized light beams after passing through the lower polarizer 122. Because the light beams transmit along the long axes of the liquid crystal molecules 131, after the linearly-polarized light beams pass through the liquid crystal layer 130, the polarizing directions of the linearly-polarized light beams remain unchanged. Thus the linearly-polarized light beams cannot pass though the upper polarizer 112, which has a polarizing axis perpendicular to that of the lower polarizer 122. As a result, the LCD 100 displays a black image.
Referring to FIG. 6, when the LCD 100 is in an on state, voltages are applied thereto, and voltage differences between the common electrode 115 and pixel electrodes 127 generate electric fields perpendicular to the first and second substrates 110, 120. Because the liquid crystal molecules 131 have negative dielectric anisotropy, they are inclined to become oriented parallel to the first substrate 110. Further, the protrusions 141, 142 affect the orientations of the liquid crystal molecules 131, such that the liquid crystal molecules 131 form inclined alignments perpendicular to the slopes of the protrusions 141, 142. Referring also to FIG. 7, the liquid crystal molecules 131 orient in four directions A, B, C and D.
In operation during the on state, incident light beams become linearly-polarized light beams after passing through the lower polarizer 122. Because of birefringence of the liquid crystal molecules 131 and the electric fields, the polarizing directions of the linearly-polarized light beams change to align with the polarizing axis of the upper polarizer 112 after passing through the liquid crystal layer 130. Accordingly, part of the light beams pass through the upper polarizer 112. Therefore, the LCD 100 displays an image with desired brightness.
Because the liquid crystal molecules 131 are oriented in four directions A, B, C and D, color shift that would otherwise be manifest in images displayed by the LCD 100 is compensated. In particular, the LCD 100 has a more even display performance along four different viewing directions corresponding to the directions A, B, C and D. That is, the LCD 100 attains a display having four domains.
However, the four-domain configuration can only compensate visual performance in four directions.
What is needed, therefore, is a multi-domain vertical alignment LCD having more domains that can provide a uniform display in more viewing directions.